The production of π∘ mesons in the reaction γ+p→π∘+p is investigated as a function of the incident γ-ray energy in the region from 200 Mev to 300 Mev. For the π∘ emitted at approximately 90° laboratory angle, the differential cross section can be represented by (dσπ∘dΩ)π2=C(K−145)1.9±0.4, where K= energy of incident γ-ray in Mev. The approximate threshold for the reaction is 145 Mev. The ratio of the cross section at 60° laboratory angle to that at 90° laboratory angle, for γ-rays between 250 Mev and 300 Mev, is 1.45±0.25.

A beam of ∼200-Mev π+ mesons was defined inside the vacuum chamber of the Nevis Cyclotron. Nuclear emulsions were exposed to a flux of about 104 mesons/cm2. The plates were scanned for pion-hydrogen scatterings and 103 such events were observed in two interaction energies, 151±7 Mev and 188±8 Mev. We obtain total cross sections of 152±31 and 159±34×10−27 cm2, respectively. The data suggest that the angular distribution changes from backwards peaked to almost symmetric over this energy interval. Our observations are not in agreement with the hypothesis of a P32-wave resonance in this energy region. The best fit to the combined results includes a D-wave contribution of -5.4°, although satisfactory agreement may be obtained with only S and P waves.

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The total proton-proton cross section (excluding Coulomb scattering) has been measured at energies from 410 Mev up to 2.6 Bev, using external beams from the Cosmotron. Fast counting equipment was used to measure the attenuation of the beams through polyethylene, carbon, and liquid H2 absorbers. At each energy E, σp−p(E, Ω) was measured as a function of the solid angle Ω subtended by the rear counter at the center of the absorber. The total cross section σp−p was obtained by a least squares straight line extrapolation to Ω=0. The measured σp−p as a function of energy rises sharply from 26.5 mb at 410 Mev to 47.8 mb at 830 Mev and then remains approximately constant out to 1.4 Bev, above which energy it decreases gradually to about 42 mb at 2.6 Bev. Using the same equipment and procedure, we have also measured the D2O-H2O difference cross section, called "σp−n," for protons over the same energy range. From a comparison of "σp−n," and σp−p, with the n−p and n−d measurements of Coor et al. at 1.4 Bev, it is apparent that one nucleon is "shielded" by the other in the deuteron. This effect is not present at energies below 410 Mev. Comparing the measured p−p and "p−n" (corrected) cross sections with the results of other high-energy experiments, one may infer the following conclusions: (1) The sharp rise in σp−p from 400 to 800 Mev results from increasing single pion production, which may proceed through the T=32, J=32 excited nucleon state. (2) Above 1 Bev the inelastic (meson production) p−p cross section appears to be approximately saturated at 27-29 mb. (3) The rise in cross section for n−p interaction in the T=0 state, associated with the rise in double pion production, implies that double meson production also proceeds through the T=32 nucleon state. (4) The probable equality of σp−d and σn−d at 1.4 Bev implies the validity of charge symmetry at this energy.

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An investigation of π−+p elastic scattering, made in a liquid propane bubble chamber, is reported. Identification of events is made on the basis of kinematics. The problem of contamination by pion scattering from protons bound in carbon is considered in some detail; it is shown that the latter requires a correction of only 4±2.5% of the total number of events. The angular distribution is presented. It shows a large diffraction peak at small angles and an approximately isotropic plateau over the backward hemisphere. The forward peak is fitted to a black-sphere diffraction pattern with a radius of (1.08±0.06)×10−13 cm. The total elastic cross section is found to be σe=10.1±0.80 mb.

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The photoproduction of charged pions from deuterium has been studied using a "monochromatic" gamma-ray beam of 292±8 Mev. The energy spectra of both positive and negative pions at the laboratory angle of 120° were determined and both agreed within experimental error with that predicted by the theory of Lax and Feshbach. The negative-to-positive ratio at 120° was 1.07±0.16, and within experimental error, was independent of meson energy. At an angle of 73° the ratio was 0.90±0.23 for 98.7 Mev mesons. The measured negative-to-positive ratio disagrees both with the simple classical picture of Brueckner and the phenomenological theory of Watson. Some results on the ratio using a bremsstrahlung beam are given.

An accurate measurement of the differential cross section for the photoproduction of positive pions from protons has been made at the Berkeley synchrotron for photon energies of 260 and 290 Mev. The mesons were produced in a thin-walled liquid-hydrogen target, and the meson-detection apparatus utilized the characteristic decay of the pion. The measurements were done in two steps, from 0° to 50° with equipment specifically designed to reduce a very high forward-angle positron background, and from 30° to 160° with equipment whose efficiency and solid angle could be accurately determined. The abrupt flattening of the observed cross section in the region forward of 40° is due to "photoelectric ejection" of pions from the cloud surrounding the nucleon. The results are compared to the theory of photo-production derived from the dispersion relations, and the agreement is satisfactory within the limitations of the theory.

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Measurements of the cross section for photoproduction of [...] mesons from hydrogen have been extended to angles as small as 5[...] in the c. m. system, using a magnetic spectrometer. At a photon energy of 1025 Mev, the cross section decreases as the angle changes from 5[degrees] to 13[degrees], reaching a minimum before increasing again to the maximum near 40[degrees] which has been previously observed (5). Less extensive measurements at energies 700, 800, 900, and 960 Mev all show a similar rapid decrease with angle in the angular range less than 15[degrees] c.m., although below 960 Mev no actual minimum is observed. These effects at small angles arise presumably from the "retardation term", or "meson current" term and its interference with other contributions to the photoproduction amplitude. It is interesting that a minimum near 15[degrees] is characteristic of the pure Born approximation (retardation term plus "S-wave"). Values of the 0[degree] cross section that are much more accurate than previous estimates have been obtained. An attempt has been made to extract a value of the pion-nucleon coupling constant by an extrapolation into the region cos [...]. Using the best set of data, the value obtained was [...].

The differential cross section for charge-exchange scattering of negative pions by hydrogen has been observed at 230, 260, 290, 317, and 371 Mev. The reaction was observed by detecting one gamma ray from the π0 decay with a scintillation-counter telescope. A least-squares analysis was performed to fit the observations to the function dσdω=Σl=15alPl−1(cosθ) in the c.m. frame. The best fit to our experimental measurements requires only s- and p-wave scattering. The results (in mb) are: The least-squares analysis indicates that d-wave scattering is not established in this energy range.

Total cross sections for negative pions on protons were measured at laboratory energies of 230, 290, 370, 427, and 460 Mev. The measurements were made in the same pion beams as and at energies identical with those of our π−−p differential scattering experiments. Comparisons of the total and differential scattering can be made with the dispersion theory at a given energy without introducing the systematic errors that would normally enter due to uncertainties in the parameters of more than one pion beam. The measured total cross sections are found to agree within statistics with other measured values, and with the sums of elastic, inelastic, and charge-exchange cross sections measured at this laboratory. The results are:

The elastic differential cross section for the scattering of negative pions by hydrogen was measured at laboratory-system pion kinetic energies of 230, 290, 370, and 427 Mev. The elastically scattered pions were detected by a counter telescope which discriminated against recoil protons and inelastic pions on the basis of range. Differential cross sections were obtained at nine angles for each energy and were fitted by a least-squares program to a series of Legendre polynomials. At the three higher energies, D waves are required to give satisfactory fits to the data. The real parts of the forward-scattering amplitudes calculated from this experiment are in agreement with the predictions of dispersion theory. The results of this experiment, in conjunction with data from other pion-nucleon scattering experiments, support the hypothesis of charge independence at these higher energies.

This paper reports experimental findings on the Dirac (F1) and Pauli (F2) form factors of the proton. The form factors have been obtained by using the Rosenbluth formula and the method of intersecting ellipses in analyzing the elastic electron-proton scattering cross sections. A range of energies covering the interval 200-1000 Mev for the incident electrons is explored. Scattering angles vary from 35° to 145°. Values as high as q2≅31 f−2 (q=energy−momentumtransfer) are investigated, but form factors can be reliably determined only up to about q2=25 f−2. Splitting of the form factors is confirmed. The newly measured data are in good agreement with earlier Stanford data on the form factors and also with the predictions of a recent theoretical model of the proton. Consistency in determining the values of the form factors at different energies and angles gives support to the techniques of quantum electrodynamics up to q2≅25 f−2. At the extreme conditions of this experiment (975 Mev, 145°) the behavior of the form factors may be exhibiting some anomaly.

The ratio of the cross sections for photoproduction of neutral pions from neutrons to that from protons has been obtained at average photon energies of 750, 875, and 1050 mev at a pion CM angle of 60° and at average photon energies of 875 and 1050 mev at a pion CM angle of 90°. The experimental technique required simultaneous detection of both the pions and the nucleons. Pions were detected by three scintillation counters. Lead plates of 2.4 radiation lengths and 1.2 radiation lengths were placed in front of the second and third counters. Neutral pions were identified by the absence of output in the first counter and the large outputs in the second and third counters. Nucleons were detected in two scintillation counters. The second of the two counters is 11” thick and has approximately 20% efficiency of detecting neutrons. Neutrons were identified by the absence of output in the first counter. The energy of the incident photons was determined by synchrotron subtraction. Since the statistical accuracy of synchrotron subtraction is poor, a system of three fast coincidence circuits was used as a time-of-flight instrument to reduce the number of events initiated by low energy photons. The statistical errors assigned to the ratio range between 15-30%. The results of this experiment agree with the results of Bingham within statistical errors, but show a general tendency for the σ^(no)/ σ^o ratio to lower. The ratio of σ^(no)/ σ^o obtained in this experiment ranges between 0.4 and 0.8. The cross sections for neutral pion photoproduction from neutrons are derived from the σ^(no)/ σ^o ratio and the Caltech data on neutral pion photoproduction from hydrogen.

Report on the investigation of interactions in π−p collisions at a pion momentum of 1.59 GeV/c, by means of the 50 cm Saclay liquid hydrogen bubble chamber, operating in a magnetic field of 17.5 kG. The results obtained concern essentially the elastic scattering and the inelastic scattering accompanied by the production of either a single pion in π−p→ pπ−π0 and nπ−π+ interactions, or by more than one pion in four-prong events. The observed angular distribution for the elastic scattering in the diffraction region, can be approximated by an exponential law. From the extrapolated value, thus obtained for the forward scattering, one gets σel= (9.65±0.30) mb. Effective mass spectra of π−π0 and π−π+ dipions are given in case of one-pion production. Each of them exhibits the corresponding ρ− or ρ0 resonances in the region of ∼ 29μ2 (μ = mass of the charged pion). The ρ peaks are particularly conspicuous for low momentum transfer (Δ2) events. The ρ0 distribution presents a secondary peak at ∼31μ2 due probably to the ω0 → π−π+ process. The branching ratio (ω0→ π+π−)/(ω0→ π+π− 0) is estimated to be ∼ 7%. The results are fairly well interpreted in the frame of the peripheral interaction according to the one-pion exchange (OPE) model, Up to values of Δ2/μ2∼10. In particular, the ratio ρ−/ρ0 is of the order of 0.5, as predicted by this model. Furthermore, the distribution of the Treiman-Yang angle is compatible with an isotropic one inside the ρ. peak. The distribution of\(\sigma _{\pi ^ + \pi ^ - } \), as calculated by the use of the Chew-Low formula assumed to be valid in the physical region of Δ2, gives a maximum which is appreciably lower than the value of\(12\pi \tilde \lambda ^2 = 120 mb\) expected for a resonant elastic ππ scattering in a J=1 state at the peak of the ρ. However, a correcting factor to the Chew-Low formula, introduced by Selleri, gives a fairly good agreement with the expected value. Another distribution, namely the Δ2 distribution, at least for Δ2 < 10 μ2, agrees quite well with the peripheral character of the interaction involving the ρ resonance. π− angular distributions in the rest frame of the ρ exhibit a different behaviour for the ρ− and for the ρ0. Whereas the first one is symmetrical, as was already reported in a previous paper, the latter shows a clear forward π− asymmetry. The main features of the four-prong results are: 1) the occurrence of the 3/2 3/2 (ρπ+) isobar in π−p → pπ+π−π− events and 2) the possible production of the ω0→ π+π−π0 resonance in π−p→ pπ−π+π−π0 events. No ρ’s were observed in four-prong events.

A magnetic spectrometer and counter telescope system was used to detect positive pions photoproduced singly in a liquid hydrogen target. Measurements of the differential cross section were made at mean laboratory photon energies, k = 1.1, 1.2, 1.3, and 1.4 GeV and in the angular range from 5° to 165 ° in the center-of-momentum system of the pion. The shape of the angular distribution of the differential cross sections at each value of k is very similar to that of the previously measured distribution at k = 1.0 GeV. The angular distributions were integrated to give the total cross sections. The third pion-nucleon "resonance" peak is seen to be very close to k = 1.0 GeV. A leveling off of the total cross section at k = 1.4 GeV may be due to the fourth "resonance". The accurate small angle data at k = 1.1 and 1.2 GeV permitted a reasonable extrapolation of the differential cross section to the pion-nucleon pole. The value of the pion-nucleon coupling constant, f, was extracted from this extrapolation. The result was f^2 = 0.078 ± 0.011.

The elastic electron-proton scattering cross section has been measured at laboratory angles between 90° and 144° and for values of the four-momentum transfer squared between 25 and 45 F−2 (incident electron laboratory energies from 830 to 1360 MeV). Both the scattered electrons and the recoil protons were momentum analyzed and counted in coincidence, making possible background-free measurements down to cross sections of the order of 10−35 cm2/sr. The data are consistent with the Rosenbluth formula, and the resulting form factors tie on well with previous measurements at lower momentum transfer, continuing the established trend.

Measurements of π0 photoproduction have been made at 235, 285, 335, and 435 MeV, using a beam of polarized x rays. Using a calculated value of polarization, an analysis is made which indicates a possible need for γ, ρ, π, or γ, ω, π coupling. The polarization calculations are checked by measurements made as a function of photon production angle at 335 MeV.

Angular distributions of recoil-proton polarization in elastic π±p scattering were measured at 523-, 572-, and 689-MeV incident pion kinetic energy. Polarization measurements were made by observing the azimuthal asymmetry in the subsequent scattering of recoil protons in large carbon-plate spark chambers. Typical strong variation of the polarization with pion scattering angle near the πp diffraction minima was observed. Since existing opinion favors a D13 resonance at 600 MeV, a phase-shift analysis was attempted in order to confirm the existence and parity of this resonance. Available πp total and differential cross sections, these polarization data, and some possible restrictive assumptions related to the 600-MeV resonance were used in the analysis. Though the polarization results aided significantly in restricting the number of acceptable phase-shift sets, still, many plausible and qualitatively different sets were found.

Angular distributions of recoil-proton polarization in elastic π±p scattering were measured at 864-, 981-, and 1301-MeV incident pion kinetic energy. Polarization measurements were made by observing the azimuthal asymmetry in the subsequent scattering of recoil protons in large carbon-plate spark chambers. The spark chambers proved to be very suitable polarization analyzer detectors. Strong variation of the polarization with backward pion scattering angle was observed.

Neutron angular distributions from the charge-exchange (π0n) and inelastic modes (π0π0n,π+π−n) of the π−−p interaction have been investigated at 313 and 371 MeV incident-pion kinetic energy. The data were obtained with an electronic counter system. Elastic and inelastic neutrons were separated in the all-neutral final states by time of flight. At both energies the charge-exchange differential cross section at the forward neutron angles differs from that determined by Caris et al. from measurements of the π0-decay gamma distributions, but generally agrees with the phase-shift-analysis calculations of Roper. The distribution of inelastic neutrons from both modes shows a strong preference for low center-of-mass neutron energies. The distribution of these neutrons does not correspond to that expected from the I=0, π−π interaction (ABC effect) suggested to account for the anomaly in p−d collisions observed by Abashian et al. Finally, all available charge-exchange differential-cross-section data from this and other experiments were combined by at least-squares fit to a Legendre expansion of the form dσdΩ*(cosθπ0*)=Σl=0NalPl(cosθπ0*) with the following results (in mb/sr):

Differential cross sections for elastic π−p scattering were measured at eight energies for positive pions and seven energies for negative pions. Energies ranged from 310 to 650 MeV. These measurements were made at the 3-GeV proton synchrotron at Saclay, France. A beam of pions from an internal BeO target was directed into a liquid-hydrogen target. Fifty-one scintillation counters and a matrix-coincidence system were used to measure simultaneously elastic events at 21 angles and charged inelastic events at 78 π−p angle pairs. Events were detected by coincidence of pulses indicating the presence of an incident pion, scattered pion, and recoil proton, and the results were stored in the memory of a pulse-height analyzer. Various corrections were applied to the data and a least-squares fit was made to the results at each energy. The form of the fitting function was a power series in the cosine of the center-of-mass angle of the scattered pion. Integration under the fitted curves gave values for the total elastic cross sections (without charge exchange). The importance of certain angular-momentum states is discussed. The π−−p data are consistent with a D13 resonant state at 600 MeV, but do not necessarily require such a resonant state.

The elastic, the pion-production, and the multipion-annihilation cross sections for antiproton-proton interactions at 3.28 and 3.66 BeV/c incident antiproton momenta have been measured. A comparison of the elastic interactions at 3.28 BeV/c with a purely-absorbing disc optical model gave a best value for the radius of interaction of 1.3 F. The real part of the forward scattering amplitude has been found to be less than 20% of the imaginary part. A study of the asymmetries in double elastic scatters yielded a value for a polarizing power of the hydrogen consistent with zero when averaged over production angles.

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Total and differential cross sections of the reaction K−p→Λη have been determined for incident K− lab momenta between 1.2 and 1.7 BeVc. No striking resonance formation in the direct channel is seen; in particular, the Y0*(2100) decays not more than 3% via the Λη channel. A prominent forward peak in the differential cross sections indicates some crossed-channel meson-exchange activity. The branching ratio Γ(η→neutrals)Γ(η→π+π−π0) is 3.6±0.6.

We have analyzed 2560 events in the final-state K O 1 K O 1 n produced in π − p interactions at 5, 7 and 12 GeV/ c . We observe the S ∗ (1070), f O and A 2 decaying into K O 1 K O 1 . Resonance parameters, cross sections, and branching ratios are given.

The cross section for the reaction [...] was measured at the Caltech synchrotron. The [...] was detected by measuring its decay gamma rays with two lead glass, total absorption Cherenkov counters. The results are three angular distributions at k = 911, 1180, and 1390 MeV, at forward angles from 3 degrees to 90 degrees. The deuteron/proton ratio differs significantly from 2.0, but final state effects from the use of a deuteron target make impossible quantitative conclusions about the neutron cross section.

Differential cross sections for the reaction π−p→π0n were measured at nine incident-pion kinetic energies in the interval from 500 to 1300 MeV. The negative pion beam from the bevatron was focused on a liquidhydrogen target completely surrounded by a cubic array of six steel-plate spark chambers. The spark chambers were triggered on events with neutral final states. Charge-exchange events were identified from the one-shower and two-shower events in the spark-chamber pictures. By the Monte Carlo technique, the π0 distributions were calculated from the bisector distributions of the two-shower π0 events together with the observed γ-ray distributions of the one-shower π0 events. These π0 distributions were fitted with both Legendre-polynomial expansions and power-series expansions by the method of least squares. The extrapolated forward differential cross sections are in good agreement with the dispersion calculations. The Legendre coefficients for the differential cross sections in isospin state T=12 were obtained by combining our results with available data on π±p elastic scattering. In the light of existing phase-shift solutions, the behavior of these coefficients is discussed. The D5F5 interference term that peaks near 900 MeV is verified to be in isospin state T=12 only. We report here also the total neutral cross sections and the cross sections for the production of neutral multipion final states 2π0n and 3π0n. The 4π solid angle and the calibrated energy response of the spark chambers contribute to the accuracy of the results.

Cross sections for the photoproduction of neutral pions have been measured at the 1.1-GeV Frascati electron synchrotron for bombarding photon energies k between 400 and 800 MeV and for π0 c.m. angles of θπ*=90∘, 120∘, and 135∘. The main feature of the experiment is good resolution in incident photon energy. The results are in good agreement with the existing theories in the energy range of 450 to 550 MeV. The cross sections exhibit a smooth behavior as a function of energy for k=400−600 MeV. No immediate evidence is found of a contribution of the P11 resonance. An anomaly at the limit of statistical significance appears for k≃700−740 MeV, indicating a possible structure of the so-called second resonance. We attempt to interpret the observed anomaly as a reflection of the sharp opening of the η production channel (η cusp effect).

The differential cross sections for single-π+ photoproduction from hydrogen have been measured over a range of momentum transfers from -2×10−4 to -2 (GeV/c)2, and photon energies from 5 to 16 GeV. The differential cross section increases by roughly a factor of 2 as the magnitude of the square of the momentum transfer decreases from 0.02 (GeV/c)2. The cross section falls approximately as exp(−3|t|) at large momentum transfers, with a similar momentum-transfer dependence of the cross section at all photon energies studied.

The π0 photoproduction cross section has been measured at 180° for photon energies from 220 to 380 MeV, in steps of 20 MeV, by detecting the recoil proton at 0°. The statistical accuracy of the measurements varies between 3 and 7%, depending on the energy. Absolute cross sections have been deduced from a comparison of the measurements with electron-proton scattering. The experimental data are compared with theoretical results calculated from fixed-momentum-transfer dispersion relations. Special attention is paid to the prediction of the multipoles at the first resonance, namely, E1+32, M1+32, and E0+π0 to obtain agreement with experiment.

Cross section angular distributions for [...] photoproduction from hydrogen were measured for 28 laboratory photon energies from 574 to 1211 MeV. At most energies, the [...] center of mass angle was varied from 60[degrees] to 170[degrees] in steps of 10[degrees]. A magnetic spectrometer was used to measure the momentum and angle of the recoil proton. A scintillation counter hodoscope with lead convertors was used to detect the presence of at least one of the [...] decay gamma rays. For a majority of the measurements the [...] rates were separated from a contamination of pi pair rates using the difference in their distribution among the gamma counters. For the remainder of the measurements, charged pi pairs were eliminated using veto counters in front of the gamma counters. Internal inconsistency and comparison with other experiments indicate that the veto data are 10 to 15% low near 90[degrees] in the region of 750 MeV. The remainder of the data show good internal consistency and fair agreement with data of other experiments. The results show a peak at 140[degrees] near 1050 MeV which had been expected but not previously measured. Comparison of the backward angle data with that from experiments measuring cross sections very near 180[degrees] indicates either an inconsistency between experiments or a rapid drop in the cross section near 180[degrees] in the region around 800 MeV.

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The polarization parameter in elastic π−p scattering has been measured, at the Berkeley 184-in. synchrocyclotron, with the use of a polarized proton target. At 318-, 337-, and 390-MeV incident pion kinetic energy, the angular range from 70° to 180° in the center-of-mass system was covered. At 229 MeV, polarization measurements were made in the angular range 150° to 180°. Phase-shift analyses, using these and other published data, were made at the two lowest energies.

We have investigated the photoproduction process γ+p→π++n over a wide range of energies and u values at the Stanford Linear Accelerator Center (SLAC) accelerator. We also have investigated γ+p→π−+N*++ at one value of u and γ+p→K++Λ0, Σ0 at one u value and three energies. Our results for dσdu for the photoproduction of π+ mesons from hydrogen are roughly α2π of the corresponding cross sections for the elastic scattering of π− mesons from hydrogen. The u dependence of our cross sections is not dominated by nucleon exchange as it is in the case of π+p elastic scattering.

The production of N ∗ (1400) isobar in the reaction pp → pN ∗+ (1400), where N ∗ (1400) → n π + and p π 0 , is investigated with the aid of one-pion exchange model. The one-pion exchange mechanism does not seem to dominate the production process. The isospin of N ∗ (1400) is found to be I = 1 2 , and the elasticity of the resonance is estimated to be 0.66.

The differential cross section for neutron-proton elastic scattering was measured in the diffraction region with incident-neutron momenta between 8 and 30 GeV/c. The experiment was a spark-chamber-counter experiment, conducted at the alternating-gradient synchrotron. Results are presented and compared with currently available lower energy np data and comparable energy pp data.

A systematic survey of strange-particle final states produced by 8−BeVc protons was made in the BNL 80-in. hydrogen bubble chamber. Cross sections were measured for some 33 reactions. The ratio of the cross section for the KK¯ channels to the total strange-particle cross section was measured to be 0.12 and appears to be rising in this momentum region. The total cross section for strange-particle production is estimated as 1.8±0.2 mb. Comparison is made of the data with the predictions of the one-pion-exchange model, and at least partial agreement occurs for the K+pΛ and πKNΣ final states. The KpΣ states appear to contain N*(1924)→KΣ, and the πKNΛ states all include Y*(1385) production with the π+K0pΛ state also containing N*(1236) and K*(890) production. An examination of the five- and six-body K, Λ states indicates strong Y*(1385) and N*(1236) production. Finally, all final states containing a K and a Λ show a dependence on M(K,Λ) which is well parametrized by a Breit-Wigner shape with M0=1777 MeV and Γ=345 MeV. This behavior is interpreted as being consistent with one-pion exchange as the dominant mechanism for these reactions.

Results are presented on measurements of elastic proton-proton scattering at 19.2 and 21.1 GeV/ c in the angular region where previously structure had been observed at lower energies.

The differential asymmetry ratio for the process γ+n→p+π− was measured at 90° in the center-of-mass system and for incident photon energies from 352 to 550 MeV. The observed asymmetries are larger than the values predicted from the theory by Berends, Donnachie, and Weaver. A smaller M1- amplitude gives better agreement between the experiment and the theory.

The cross section for γp→π−Δ++(1236), measured at 5, 8, 11, and 16 GeV from nearzero momentum transfer to -1 GeV2 (-2 GeV2 at 16 GeV), rises from small t to a maximum near −t=mπ2, then falls as e12t out to −t≈0.2 GeV2, after which it becomes roughly equal in slope and magnitude to the single π+ photoproduction cross section (e3t). At fixed t, the cross section varies as k−2, where k is the laboratory photon energy. The results do not agree well with the simple vector-dominance model.

We have studied the ratio R=[dσ(γd→π−pp)dt][dσ(γd→π+nn)dt]−1 at 8 and 16 GeV for momentum transfers |t| from about 0.001 to 1.3 GeV2. R is close to unity for |t|<mπ2, but falls very rapidly with increasing |t|, passing through ½ near |t|=0.1 GeV2 and having a minium value of about 13 near |t|=0.4 GeV2; it slowly increases at larger momentum transfers. These results are similar to those obtained in other laboratories at 3.4 and 5 GeV. This implies considerable interference between the isoscalar and isovector photon amplitudes.

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Differential cross sections for the elastic scattering of negative pions from hydrogen have been measured over a limited range of squared four-momentum transfer (t) in the vicinity of t≃−3 (GeV/c)2 for incident pion momenta of 2.51, 2.76, and 3.01 GeV/c. These measurements confirm the existence of a minimum in the differential cross section in this region of incident momentum and scattering angle. The minimum occurs at a smaller value of t [t≃−2.6 (GeV/c)2] than has been observed at higher momenta.

The differential cross sections for the elastic scattering of negative pions by deuterons have been measured for 2.01-, 3.77-, and 5.53-GeV/c incident pion momenta, over an interval of the squared four-momentum transfer from -0.25 (GeV/c)2 to ∼-1.0 (GeV/c)2. The results are consistent with calculations based on a Glauber model of the scattering process.